which Federal official was to be directly elected by voters according to the original US Constitution

Passed by Congress May 13, 1912, and ratified April 8, 1913, the 17th amendment modified Article I, section 3, of the Constitution by allowing voters to cast direct votes for U.S. Senators. Prior to its passage, Senators were chosen by state legislatures.

the answer is 250 percent.

the causes of the dust bowls were severe droughts,   lands became dry and hard, temperature was higher than usual, hot and dry conditions killed crops, high winds. because of those factors, the winds kicked up dry soil and created clouds of dust.